Selective audion-amplifier



Patented Nov. 22,1921.

l.. DE FOREST.

SELECTIVE AUDION AMPLIFIER.

APPLICATION FILED APR. 9, 191:

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LEE mt FOREST, 0]? NEW YORK, N. Y., ASSIGNOR TO DIE FOREST RAD IOTELEPHONE AND TELEGRAPH GOMPAN Y, OF NEW YORK, N. Y.,'A CORPORATION OFDELAWARE- SELECTIVE AUDION-AMPLIFIER.

T 0 all whom it may concern:

' Be it known that I, LEE DE FOREST, a citizen of the U 'ted States,residin at New York, county f Bronx, State of ew York, have made acertain new and useful Invention in Selective Audion-Amplifiers, ofwhich the following is a specification.

This invention relates tov selective audion amplifiers.

The object of the invention is to provide an audion amplifier andsuitable circuit arrangements associated therewith which willselectively amplify currents I impressed thereon.

A further object of the invention is to provide an arrangement of theclass referred to which will selectively amplify currents of a highfrequency to a greater degree than currents of a lower frequency.

Further objects of the invention will appear more fully hereinafter.

The invention consists substantially in the combination, location, and

more fully hereinafter set forth, as shown on the accompanying drawingand finally pointed out in the appended claims.

Referring to the drawing,

Figure 1 is a diagrammatic view of a receiving or relay stationembodying my 'invention.

Figs. 2 and 3 show modified circuit arrangements for accomplishing thepurposes and embodying the principles of my inven tion.

The same part is designated by the same reference character wherever itoccurs throughout the several views.

It is well known that in long distance telephonic or telegraphiccircuits, especially where many miles of cable conductors are employedas distinguished fromtradio communications, a distortion of thetelephonic or telegraph signal currents is observed, due to thedistributed capacity of the line wire or cable. This is particularlytrue of the telephone lines. The higher frequency currents areattenuated at a greater rate than those of lower frequencies, so thatthe reproduction of the voice at the distant receiving station becomesfaulty or unintelligible, To counteract this at enuation of ISpecification. of Letters Patent. l afnfed NQV, 22, 1921. Applicationfiled April 9, 1915. Serial No. 20,173. 4 i

the higher frequencies by the distributed capacity of the line,artificial inductance,-

to their original or nearly original amplitudes at the receivingstation.

In accordance with my invention, I propose to employ a well known formof audion amplifier, such as is shown and described in my Letters PatentNo. 841,387, issued to me on January 15, 1907, and soassociating circuitarrangements therewith that the audion will perform its amplifyingfunction selectively; in other words, incoming "currents, or currents ofcertain frequencies received by the audion will be amplified to agreater degree than currents of other frequencies, and especially,currents of lower frequencies. In addition, thereto, the prim ciple ofselective amplification, can be emphasized as much as is desired ornecessary,

' so that, if desired, the normal voice currents before going in on atelephone line can first be distorted and the higher harmonics thereofmade of greater amplitudes so that after these latter currents arereduced in amplitude by the distributed capacity of the telephone line,the composite current will arrive at the distant receiving station inits normalor original form.

In applyin my invention, the selective audion ampli er may be introducedat several intermediate points along the line so as to restore thewasted higher frequency components of the current waves, before theyhave been completely attenuated bythe distributed capacity of a'longline.v Thus, for

example, in a telephone line extending saythree thousand miles, aselective audion amplifier may be installed at ten'points along the lineat approximately three hundred miles apart, so arranged and tuned as Ishall hereinafter describe, and the telephonic or voice currents willleave each separate station reinforced in amplitude and with a wave formsimilar to the original form at the first or sending station.

Referring to the drawing Reference character 1desig nates an exhaustedaudion bulb of the usual and well known double plate and grid typewherein is 'located the usual filament F which is heated from thecurrent source A and controlled by the variable resistance R. The gridelements or input electrodes G, G, are preferably arrangedon either sideof the filament F, and, as shown in Figs. 1 and 2, are connected inparallel. The wing, or plate electrodes IV, IV, are also arranged on resectively opposite sides of the filament F, an at a different distancetherefrom relative to the grid electrodes G, .G. The incom-' ing currentto be amplified is led from the line to the rimary coil S, of atransformer T, preferab y a step-up transformer. While I am not to belimited to the specific arrangement shown, I prefer to have the secondary coil of the transformer T wound in two parts disconnected fromeach other as shown at O, the parts therebypossesslng a large capacityrelative to each other. One end of one windin of the secondary 0011 ofthe transformer 'I is connected directly to the filament F of the audion1, while one end of the other coil is connected to the gr1ds G, G, ofthe audion 1. If desired, 1n the transformer and grid circult, acondenser may be inserted, as shown in dotted lines at P. The plate' orwing electrodes W, W, are

transformer V to one terminal, preferably the positive terminal of asource of current such as a battery B, the other, preferably thenegative, terminal of which is connected to the filament F of audion 1.The outgolng or live circuit L is connected to the secondary of thetransformer V. 1

An oscillating circuit consisting of the inductance E and capacity H isconnected by one terminal to the wing or plate electrodes W, W, and 'bythe other terminal to the grid electrodes G, G. If desired, and asshown. a capacity preferably in the form of a variable condenser C, maybe Inserted 1n this circuit. I prefer to insert a variable dampingresistance J y in lead of this circuit to the grid electrodes. Theobject of this damping resistance is to reduce the amplitude of thepotential sures delivered from the oscillating circuit H, I), to thegrid electrode, as above described.-

The natural period of vibration of this oscillating or parasitic circuitdepends to a great extent upon the amount of inductance of the coil Eand the amount of the capacity of the condenser H. This frequency alsodepends upon the constants of the audion itself, the brightness of thefila- 65 ment F, the applied potential from the batconnected through aninductance coil of a thereof shown and described.

In addition to the first oscillating or par asitic circuit, if desired,a second similar circuit comprising the elements C, J, E, H, identicalwith the corresponding elements of the first circuit, maybe connectedbetween the grid and plate electrodes, but the oscillating circuit E, H,should be tuned to a different frequency, or natural rate of oscillationthan that of the first oscillating circuit. Similarly, any number ofoscillating circuits, each tuned to a different frequency, canbeconnected to the audion.

It is not necessary, however, to connect such a parasitic or reinforcingcircuit to the audion for each different frequency it is desired toamplify. I have found that one such circuit, the natural fundamentalfrequency of which may be such as to cause it to tend to oscillateapproximately .1500 times per second, will cause incoming currentshaving frequencies considerably higher 100 than 1500 to be amplifiedalmost to the same degree while at the same time notpermitting currentshaving considerably lower frequencies to be thus auto-amplified. I havefound that two such reinforcing circuits, the natural period of one ofwhich is such as would cause the audion to deliver a sus; tained note ofa frequency of about 1500 per second," if free to oscillate; and thenatural period of the other of which is such as would cause the audionto deliver, if free to oscillate, a sustained note of about 2500 persecond, will reinforce currents of all frequenciesbetween 1200 and 3000per second. It is therefore possible to arrange 'asingle audion- 115with reinforcing circuits to so selectively amplify voice currents thatall the higher harmonics are amplifiedover those of the lower orfundamental frequencies.

The principles involvedin enabling an in certain arrangements the audionwill set up, or tend to set up in such oscillating orseml-osclllatingcircuits, oscillating or pulsating currents which are or tend to becomeself-per tuating. Such currents .then rapidly bull up to relativelylarge amplitudes. It frequently happens, unless special means be takento prevent it, that these oscillating or pulsating currents persist,setting up a sustained singing note in the telephone receiver connectedwith" the audion. This of course is objectionable, and it is easy "toprevent this by introducing into the pulsating current circuit, dampingelements such as a high resistance which while not completely annullingthe tendency of such circuits to oscillate and to amplify currentspossessing their natural or individual frequency, nevertheless preventthe persistent automatic oscillation of'those circuits.

In Fig. 2 I show another circuit arrange ment used in connection with anaudion for amplifying currents of certain fre quencies to a greaterdegree than other currents having lower frequencies. In this form of myinvention the two oscillating circuits contain inductances X and X thecapacities C and C and the damping resistances J and J respectively.These two circuits are connected in parallel across the grid andfilament electrode terminals of the audion amplifier 1. Each of theseinductances are associated with an inductance Z in the out-put or plateelectrode circuit. With this arrangement of circuits, the audion wouldbecome the source of persistent oscillating currents set up in the Wingor plate circuit and reflected back upon the grid circuit to be againamplified were it not for the presence in said circuits of the dampingresistances J and J Nevertheless these circuits possess the tendency toamplify currents impressed upon the audion from the source provided thefrequencies of these currents approximate those of the reflection orreinforcing circuits. In Fig. 3 'I have shown another circuitarrangement for accomplishing the objects of my invention wherein theincoming currents are conducted to one of the grid electrodes, as G. Oneof the wing or plate electrodes W is connected to the outgoing line inthe usual manner hereinbefore described. The oscillating or reinforcingcircuits are connected to the other electrodes W G of the audion bulb 1.Each of the oscillating circuits contains a common inductance Xassociated with the coil Z in the output circuit in the manner shown anddescribed in Fig.

2. The individual inductances E, E E

etc., each in series with a capacity H, H H etc., respectively determinethe period of the reinforcing circuits, on which in this figure I haveshown three. The effect of these reflection circuits associated with theout-put circuit is to impart to the audion a tendency todisproportionately amplify currents having frequencies generallyapproximately those of the three reinforcing circuits. In thisarrangement the usual damping resistance J is inserted in the comsameresults Without departing from the scope of my invention as defined inthe claims.

What I claim as new and useful and of my own invention, and desire tosecure by Letters Patent, is,-

1. An amplifier, including an input and an output circuit, and aplurality of oscillating circuits associated therewith to selectivelyamplify the current of certain frequencies in the input circuit.

2. An amplifier, including an input and an output circuit, circuit.connections therefor, and means associated therewith to selectivelyamplify the current of certain frequencies in the input circuit.

3. An amplifier, circuit connections therefor includin input and outputcircuits, and means associated therewith to amplify currents of certainfrequencies impressed on the input circuit to a greater degree thanother frequencies impressed on the input circuit.

4. An amplifier, an input and an output circuit therefor and a pluralityof oscillating circuits associated therewith to amplify impressedcurrents of certain input frequencies to a greater degree than impressedcurrents of other frequencies. 5

5. An amplifier, circuit connections therefor including input and outputcircuits, and means associated therewith to amplify currents of'certainfrequencies impressed on the input circuit to a greater degree thancurrents of lower frequencies impressed on the input circuit. j

6. An amplifier, an input and an output circuit therefor and a pluralityof oscillating circuits associated therewith to amplify impressedcurrents of certain input frequencies to a greater degree than impressedcurrents of lower frequencies.

7. In an audion repeater system, an audion comprising a hot electrodeand cold electrodes, an input circuit associated with one cold electrodeand an output circuit associated with the other cold electrode, and aplurality of oscillating circuits connecting said cold electrodes.

8. In an audion repeater system, an audion trodes, an in ut circuitassociated with one cold electro e and an output circuit associatedwitlr the other cold electrode, and a plurality (if oscillating circuitsconnecting said cold electrodes, and means for damping each of saidoscillating circuits.

10. In an audion repeater system, an auof cold electro es, input. andoutput circuits associated with said audion, and a plurality ofoscillating circuits connected between said cold electrodes and meansfor damping each of said oscillating circuits.

11. In an audlon repeater system, an audion comprising a hot electrodeand cold my hand this 7th clay electrodes, an input circuit-associated vvith circuits "connecting sald cold electrodes, an

dion jcomprisin "a hot-electrode' and two sets dion comprisin a. hotelectrode and two sets of cold electro' es,'input and output circuits II avariable' resistance nserted 1n each of' said osclllating 'clrcults.v12. In. an audmn repeater system, an .au-.

associated with said audion, and aplurality 1 of os'cillatin circuitsconnectedbetweensaid sertedi in each of said oscillating circuits.

In testimony'whereof I have hereunto set 30 of April, A. D. 1915, LEE on'F'QBEST.

